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# Iterators, Hashes, and Arrays

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Iterators, Hashes, and Arrays

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• 5 is an object that is an instance of the integer class\ntimes is a method of the 5 object\ntimes is a method on an object that is an instance of integer\n
• A lot of the time you will be using an array when you iterate over something\nAn array is just a list of items. \nEvery spot in the list acts like a variable and you can make each spot point to a different object\n\nW means words\n\nArray is a class, needs to start with capital letter\n
• IRB\nif you go off the array it will be nil\n
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• join is cool because it makes a string for you\n\nshovel operator\n\nmultidimensional array\n
• Does anyone know what a hash is? \nassociative array \ncollection of key-value pairs\nkeys can be numbers or strings \n\nDifference from an Array\n
• merge takes the value from the second hash\nmerge! changes h1\n
• you would think that delete should need a bang to change the hash, but delete doesn&amp;#x2019;t exist with a bang\ndelete returns the value\n
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• ### Iterators, Hashes, and Arrays

1. 1. COLLECTIONS & ITERATORS WITH HASHES AND ARRAYS Sarah Allen
2. 2. ITERATORS: CONDITIONAL LOOPING• “while” allows us to loop through code while a set condition is true x = 1 while x < 10 puts x.to_s + “ iteration” x += 1 end
3. 3. TIMES5.times { puts “hello” }5.times { |num| puts “hi”+num.to_s }99.times do |beer_num| puts "#{beer_num} bottles of beer”end99.times do puts "some bottles of beer”end
4. 4. CREATING A NEW ARRAY x = [1, 2, 3, 4] => [1, 2, 3, 4] x = %w(1 2 3 4) => [“1”, “2”, “3”, “4”] chef = Array.new(3, “bork”) => [“bork”, “bork”, bork”]
5. 5. ACCESSING ARRAY VALUESa = [ "a", "b", "c", "d", "e" ]a[0] #=> "a”a[2] #=> "c”a[6] #=> nila[1, 2] #=> ["b", "c”]a[1..3] #=> ["b", "c", "d”]a[1…3] #=> ["b", "c"]
6. 6. RANGESInclusive1..4# => runs 1 thru 4(1..4).to_a# => [1,2,3,4]Exclusive1...4# => runs 1 thru 3(1...4).to_a # => [1,2,3]
7. 7. OPERATIONS ON ARRAYS[ 1, 2, 3 ] * 3=> [1, 2, 3, 1, 2, 3, 1, 2, 3][ 1, 2, 3 ].join(“,”)⇒ "1,2,3”[ 1, 2, 3 ] + [ 4, 5 ]=> [1, 2, 3, 4, 5][ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]=> [3, 3, 5][ 1, 2 ] << "c" << "d" << [ 3, 4 ]=> [1, 2, "c", "d", [3, 4]]
8. 8. CREATING A HASHh = { "a" => 100, "b" => 200 }h["a"]h = { 1 => "a", "b" => “hello” }h[1]
9. 9. OPERATIONS ON HASHES: MERGEh1 = { "a" => 100, "b" => 200 }=> {"a"=>100, "b"=>200}h2 = { "b" => 254, "c" => 300 }=>{"b"=>254, "c"=>300}h3 = h1.merge(h2)=> {"a"=>100, "b"=>254, "c"=>300}h1=> {"a"=>100, "b"=>200}h1.merge!(h2)=> {"a"=>100, "b"=>254, "c"=>300}
10. 10. OPERATIONS ON HASHESh = { "a" => 100, "b" => 200 }h.delete("a”)h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }letters = h.keysh = { "a" => 100, "b" => 200, "c" => 300 }numbers = h.values
11. 11. EACH>> superheroes = ["catwoman", "batman", "wonderwoman"]>> superheroes.each { | s | puts "#{ s } save me!" }catwoman save me!batman save me!wonderwoman save me!>> dogs = ["fido", "fifi", "rex", "fluffy"]>> dogs_i_want = []>> dogs.each do |dog|>? dogs_i_want.push(dog) if dog != "fluffy">? end>> dogs=> ["fido", "fifi", "rex", "fluffy"]>> dogs_i_want=> ["fido", "fifi", "rex"]
12. 12. MAPsuperheroes = ["catwoman", "batman", "wonderwoman"]>> superheroes.map { |s| s.upcase }=> ["CATWOMAN", "BATMAN", "WONDERWOMAN"]Shorter (available in Rails or Ruby 1.8.7+):>> superheroes.map(&:upcase)